Implantable medical devices, for example cardiac pacemakers and defibrillators, often include elongate medical electrical leads having one or more electrodes to sense electrical activity and deliver therapeutic stimulation. With the advent of left ventricular pacing to alleviate heart failure, leads have been advanced into the coronary veins in order to position the electrodes of the leads at left ventricular pacing sites, typically located in proximity to the base of the left ventricle. Although a variety of left ventricular pacing leads, along with methods for implanting such leads, have been developed, there is still a need for a lead including features that facilitate delivery to, and fixation at, sites in the coronary vasculature.
Numerous types of medical electrical leads can be adapted for placement in the coronary vasculature. Exemplary active fixation leads include U.S. Pat. No. 7,860,580, issued to Sommer, et al., U.S. Pat. No. 7,532,939, issued to Sommer, et al. and U.S. patent application Ser. No. 13/793,622, filed Mar. 11, 2013 by Sommer, et al., all of which are incorporated herein by reference in their entirety. Shaped leads can also be adapted for placement in the coronary vasculature. Exemplary shaped leads or catheters include U.S. Pat. No. 7,313,444, issued to Pianca et al., U.S. Pat. No. 5,387,233, issued to Alferness, et al., U.S. Pat. No. 5,925,073, issued to Chastain, et al., U.S. Pat. No. 6,430,449, issued to Hsu, et al., U.S. Pat. No. 6,129,750, issued to Tockman et al., U.S. Pat. No. 6,321,123 issued to Morris. The self-anchoring lead disclosed in Pianchi et al. includes radially spaced electrodes that are electrically active around their circumference, which can result in unwanted phrenic nerve stimulation. It is desirable to develop a coronary sinus lead that does not inadvertently cause phrenic nerve stimulation.